Conductivity measurements on liquids are performed by applying a AC voltage across a pair of electrodes. The frequency may range from 50 Hz up to 50 kHz, depending on the electrolyte concentration in the sample. Thereby measurement errors frequently occur due to interfering phenomena at the electrodes, where a polarization effect occurs, in that ions having the same charge form layers on the electrode surfaces. This yields an additional capacitance, the so called "double-layer-capacitance". In order to minimize the influence of this interfering capacitance, one can increase the measurement frequency with increasing salt concentration.
Instruments presently available utilize a few fixed frequencies, commonly three or four, for different sensitivity ranges. Switching between the different measurement frequencies takes place automatically in dependence of the salt concentration. A disadvantage with this known method is that the various capacitances will not balance out optimally because of the limited frequency options available.